All-electric A.C. tractor

ABSTRACT

An electronic differential speed control circuit for driving the inboard and outboard A.C. wheel motors at different relative speeds depending upon the steering angle during a turn. An electrical circuit for sensing the torque of the tractor&#39;s wheel motors to maintain a constant implement draft. A hollow tubular axle pivots around the tractor&#39;s longitudinal material-transferring tunnel to conserve space and permit mounting of the wheel motors within the axle. The tunnel has two material-transferring compartments or passageways, and has vertically movable extensions on either end to facilitate coupling to accessories. An electrical power outlet is provided for energizing non-motor driven accessories.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.769,378 filed Feb. 16, 1977, (now U.S. Pat. No. 4,113,045) the benefitof which is claimed as provided by 35 USC 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of farm tractors havingaccessories driven by power supplied by the tractor and, moreparticularly, to an all-electric tractor having an A.C. power sourcewhich provides power both for energizing induction motors for drivingthe tractor's wheels and also for energizing electric accessoriesassociated with the tractor.

2. Description of the Prior Art

The wheels or other traction means of farm tractors or other landvehicles have traditionally been driven by internal combustion enginesthrough mechanical coupling means, including complex transmissions.Furthermore, accessories were mechanically driven by a power-take-off(PTO) driven by the engine. It is also broadly known to drive the wheelsof a land vehicle by A.C. induction motors controlled bycycloconverters. In addition, there has recently been developed a logstacker whose wheels are driven by D.C. motors and whose log handlingmechanism is driven by A.C. motors. Also, there has been disclosed theconcept of driving the wheels of both a truck and its trailer byindividual wheel motors powered by a generator located in the truck.

Examples of such prior art systems are found in the following U.S.patents and publications:

    ______________________________________                                        Patents                                                                       U.S. Pat. Nos.                                                                ______________________________________                                        3,577,050     Ringland et al                                                                              May 4, 1971                                       3,584,276     Ringland et al                                                                              June 8, 1971                                      3,690,395     Spiller et al Sept. 12, 1972                                    3,713,504     Shimer et al  Jan. 30, 1973                                     3,860,081     Moll et al    Jan. 14, 1975                                     ______________________________________                                    

PUBLICATIONS

An A-C Individual Wheel Drive System for Land Vehicles, Document 660,134(undated), by Walter Slabiak, U.S. Army Tank-Automotive Center, pp.664-671

"Precise Control of a Three-Phase Squirrel-Cage Induction Motor Using aPractical Cycloconverter", Slabiak and Lawson, dated July/August, 19?,IEEE Transactions on Industry and General Applications, Volume 2, No. 4

"Optimal Control, System Performance for an A-C Electric VehicularDrive", Lawson et al, Power Equipment Div., Lear Siegler, Inc., Document660,135 (undated)

Le Tourneau Letro-Stacker Product Circular, dated September 1969

SUMMARY OF THE INVENTION

The primary object of this invention is to provide an all-electric A.C.tractor system wherein the tractor's wheels are driven by controllableA.C. induction motors and wherein other accessories are energized bypower derived from an A.C. power supply carried by the tractor.

A more specific object of this invention is to provide such a tractorsystem wherein the A.C. power supplied to the wheel induction motors arecontrolled by a cycloconverter and also by an electronic differentialspeed control circuit which automatically drives the inboard andoutboard wheels of the tractor at different relative speeds inaccordance with the steering angle of the tractor.

Another object of the invention is to provide such a tractor with alongitudinal material-transferring tunnel having a vertically movableextension at one end thereof.

Another object of the invention is to provide such a tunnel with twoseparate compartments for transferring different materials at the sametime.

Another object of the invention is to provide such a tractor withtubular axles in which the wheel drive motors are mounted, therebysaving space over prior art designs.

Still another object is to construct such a tubular axle so that itpivots about the material transferring tunnel.

Still another object of the invention is to provide such a tractorsystem with one or more A.C. and/or D.C. power outlets from whichnon-motor driven electric accessories can be energized.

Another object of the invention is to provide such a tractor system witha torque demand monitor circuit coupled to the circuit of a wheeldriving motor to determine drive wheel torque and in turn control thelift on the front or the rear of the tractor in accordance with apredetermined amount of implement draft.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1a is a side view of a tractor embodying this invention and showsparticularly the vertically adjustable extension of the longitudinalmaterial-transferring tunnel.

FIG. 1b is a perspective view of the tractor illustrating in more detailthe material-transferring tunnel which can also be used to attach andlift implements.

FIG. 2a is a side view of the material-transferring tunnel removed fromthe tractor to better illustrate the vertically movable extensions.

FIG. 2b is a sectional view of FIG. 2a illustrating the tubular axlehousing in which a drive wheel motor is mounted and wherein the axle ispivoted about the material-transferring tunnel of the tractor andshowing the improved material-transferring tunnel having twocompartments.

FIG. 3 is a schematic diagram illustrating an embodiment of thedifferential wheel driving circuit of the invention.

FIG. 4 is a schematic diagram of an individual drive wheel torquemonitoring circuit embodying the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

My invention consists of improvements on the all-electric A.C. tractordisclosed and claimed in the aforesaid allowed copending applicationwhich is expressly incorporated herein by reference.

FIGS. 1a and 1b show a tractor as illustrated in the aforesaid pendingapplication but including the improvement of vertically movable tubes 10and 11 which form extensions of the material-transferring tunnel 12 (seeFIG. 2a) which extends from the front to the rear of the tractor alongthe longitudinal center line thereof. In this improvement, instead ofthe material-transferring tunnel being formed by a straight tube as inthe aforesaid pending application, at least one extension tube 10 or 11is connected to the tunnel 12 by a flexible joint 13 or 14 at at leastone end of the tunnel so that the tube can be adjusted verticallyrelative to the fixed portion of the tunnel. The flexible joint 13, forexample, includes a pivot pin 15 on either side of the tunnel and abellows assembly 16, and lifting cylinders 17 accomplish the verticaladjustment of the tube 10 and replace the lifting arms or forks 70 shownin the aforesaid pending application. The flexible joint 14 is ofsimilar construction comprising a pivot pin 18 on either side of thetunnel and a bellows assembly 19 with lifting cylinders 20 providingvertical adjustment. Thus, the material-transferring tunnel, and inparticular the extension tube 10 or 11, becomes both the lifting andmaterial-transferring means for any modular accessory connected to thetractor. A material-transferring means, such as an auger or screwconveyor 12a with suitable universal joints, transfers the materialthrough the tunnel from the front to the rear of the tractor. Such anarrangement also eliminates the problem of a change in distance ortunnel length between the tractor and accessory. The problem with theadjustable lift arms or forks of said copending application was that thearms pivoted at a point different from that at which the accessoryjoined the tunnel, thereby requiring a telescopic tunnel section betweenthe tractor and the accessory.

As particularly shown in the cross-sectional view of FIG. 2b, the tunnelhas two individual material-transferring compartments or passageways 21and 22 so that several types of material, such as grain and chaff, canbe transferred simultaneously. The tunnel may have more than twocompartments. For example, two smaller compartments may be used forconveying grain, and a larger compartment for conveying chaff. In use,there would be a conveying means associated with the tunnel. Suchconveying means can be either mechanical, such as augers or screwconveyors 21a and 22a, or chain and flight or flat belts, or pneumaticmeans, wherein the material is conveyed by air pressure. The tractorwould also be provided with a material-receiving means, such as acontainer 116, which is carried on the tractor or pulled behind, orboth, for example where the crop is stored in one container and the cropresidue in another. A blower 118 elevates the material through adischarge spout 120 and blows it into the container 116.

FIG. 2b also illustrates the improved rear axle and wheel motor mountingarrangement. The hollow tube axle 23 has a circular enlargement 24 inthe center thereof which surrounds the tractor tunnel 12 and oscillatesthereabout. By contrast, in the tractor of the aforesaid copendingapplication, the rear axle oscillated on a center hinge point directlyabove the tunnel, thereby occupying a great deal of space where itcrossed the tunnel and not permitting the mounting of the traction orwheel motor within the axle. In the improvement shown in FIG. 2b, theaxle is tubular or hollow, and the axle is concentric with the center ofthe tractor wheels. With this improved arrangement, the wheel drivingmotors 25 are mounted inside the axle 23. Furthermore, with thisarrangement, the front and rear axle assemblies are identical, eventhough only one is permitted to pivot freely. An advantage of thisarrangement is that, if either the front or rear axle is left free topivot with the terrain, the other can be mounted rigidly to the frame,or it can be outfitted with hydraulic cylinders so the tractor can beleveled from hillside operation.

FIG. 3 shows the preferred embodiment of the differential wheel speedcontrol circuit of the invention and represents an improvement on thewheel control circuit shown in FIG. 2 of the aforesaid co-pendingapplication. As shown in said co-pending application, there are mountedon the tractor a prime mover and a three-phase alternator whose A.C.output is applied to left and right cycloconverters which control theright and left wheels, respectively, of the tractor. Even though it istrue that the circuit shown in said co-pending application provides acertain amount of differential wheel speed control due to the motor slipof the induction wheel-driving motors, it has been found that because ofthe great amount of gear reduction necessary for meeting torquerequirements, this motor slip is not sufficient to allow short or sharpturns of the tractor.

In the improved differential speed control circuit shown in FIG. 3 ofthe present application, the speeds of the inboard and outboard wheelson a turn are directly controlled in response to the steering angle, sothat the speed of the outside wheels is increased relative to the speedof the inside wheels in a manner analogous to a mechanical differential,with the advantage that the load does not have to be equalized as isrequired for a differential.

FIG. 3 illustrates a preferred embodiment of the improved differentialspeed control circuit. In the same manner as illustrated in FIG. 1 ofthe aforesaid copending application, a prime mover 29 on the tractordrives an alternator 30 whose A.C. output is supplied to the right andleft cycloconverters 40 and 62, respectively. A D.C. reference voltage+V is applied across a master speed control in the form of apotentiometer P1 having a fixed resistor 32 and a wiper arm 34 whoseposition on the resistor 32 determines the magnitude of the voltageV_(a) and, thus, the speed of the tractor wheels when the tractor ismoving in a straight line, i.e., when the stearing angle is zero. Theparticular voltage V_(a) picked off by wiper arm 34 is supplied to the(+) input a of an algebraic summer 36. The summer also has a (-) input band a (+) input c, together with an output d. The output voltage V₃ isamplified by an amplifier 38 and applied to the right cycloconverter 40whose A.C. output voltage V_(R) is applied to the induction motor 42which is mechanically coupled to a right wheel 44. The frequency of theoutput voltage V_(R) of the cycloconverter determines the rotationalspeed of motor 42 and wheel 44. The output voltage V_(R) is alsosupplied to a frequency discriminator 46 whose output voltage V_(fb1) isproportional to the frequency of V_(R), and the voltage V.sub. fb1 isapplied to the (-) input b of summer 36.

The output voltage V_(a) of the master speed control potentiometer P1 isalso applied to the upper end of the fixed resistor 52 of a steeringpotentiometer P2. The voltage V_(a) is also inverted by an inverter 50and applied to the lower end of resistor 52. The wiper arm 54 of thesteering potentiometer P2 is positioned along the fixed resistor 52 inaccordance with the steering angle of the tractor. When the steeringangle is zero, the wiper arm 54 is on the midpoint of resistor 52, andthus, the voltage V₂ is zero. Also, V₂ is positive when wiper arm 54 isabove the midpoint, and negative when the wiper arm is below themidpoint. The voltage V₂ is fed back through an inverter 56 as a voltage-V₂ to the (+) input c of the summer 36 in the right wheel controlcircuit. Consequently, the voltage V₃ on the output of the summer 36 isequal to V₃ =V_(a) -V_(fb1) +(-V₂).

The voltage V₂ on the wiper arm 54 is also applied to the (+) input e ofanother summer 58. The voltage V_(a) is applied to the (+) input f ofthe summer 58. The voltage V₄ on the output g of summer 58 is amplifiedby an amplifier 60 and applied to the input of the left cycloconverter62 whose A.C. output voltage V_(L) is applied to the left wheelinduction motor 64 which is mechanically coupled to a left wheel 66 ofthe tractor. The frequency of the voltage V_(L) determines therotational speed of both the motor 64 and the wheel 66. Thecycloconverter output voltage V_(L) is also applied to a frequencydiscriminator 68 which produces a feedback voltage V_(fb2) to the (-)input h of summer 58. The feedback voltage V_(fb2) is proportional tothe frequency of the left wheel motor control voltage V_(L). Thus, V₄=V_(a) -V_(fb2) +V₂.

Since the wiper arm 54 is positioned in accordance with the steeringangle of the tractor, the input voltage V₃ to cycloconverter 40 willincrease when the input voltage V₄ to cycloconverter 62 decreases, andvice versa, to provide an electronic differential speed control for theright and left wheels. More specifically, if the tractor is moving alonga straight line, i.e., the steering angle is zero, then the master speedcontrol voltage V_(a) is applied to both cycloconverters 40 and 62,since the voltage V₂ is zero. Consequently, the wheel driving A.C. motorvoltages V_(R) and V_(L) for the right and left wheels, respectively,are of the same frequency, and both the right and left wheels will berotated at the same speed. However, when the tractor is making a lefthand turn, since it is desired to drive the right or outside wheels at agreater speed than the left or inside wheels, the wiper arm 54 will movedownward so that voltage V₂ assumes a negative value dependent upon thesteering angle. Thus, the magnitude of voltage V₂ will be added to thespeed control voltage V_(a) in summer 36, and subtracted from V_(a) insummer 58, whereby the voltage V₃ is larger than the voltage V₄. Thus,the frequency of voltage V_(R) is greater than that of voltage V_(L),and the right wheel motor 42 rotates faster than the left wheel motor64.

In a wheel tractor the wiper arm 54 of the potentiometer P2 iscontrolled by the steering action of the tractor. Specifically, in anon-articulated tractor the wiper arm 54 is mechanically controlled bythe movement of the tie rod or directly from the steering shaft. In anarticulated tractor, the angle of steering is determined at the pointwhere the front and back halves of the tractor are connected, and thepotentiometer P2 is typically mounted on one tractor half, with thewiper arm 54 mechanically connected to the other tractor half.

A crawler tractor, as opposed to wheel tractor, is controlled in asimilar manner, with the exception that a crawler tractor is actuallysteered by the speeding up and slowing down of the tracks on theopposite sides of the tractor. In a crawler tractor, the steering actionis controlled by the relative speeds of a right and left traction motor.As the manual steering control is operated, it will produce a turn inaccordance with the distance the steering control is moved from itsneutral or straight ahead position. The greater the distance thesteering control is moved in one direction, the slower the track on oneside will move and the faster the track on the other side will move.Thus, the wiper 54 is simply mechanically connected to the steeringcontrol.

FIG. 4 illustrates the improved torque demand monitoring and controlcircuit which is coupled to the two input leads of a wheel-drivinginduction motor.

Input leads 80 and 82 supply the frequency varying A.C. voltage from thecycloconverter to an induction wheel-driving motor 84. The input orapplied voltage V to the motor is applied via leads 86 and 88 to aconventional motor torque computer 90. The current I flowing to themotor 84 is sensed by means of a current sensor 92 coupled to one of themotor input leads, such as lead 82. The current sensor produces avoltage proportional to the current, and this voltage is also applied tothe computer 90. The current sensor may be a current transformer or anyother suitable current-to-voltage transducer. A tachometer 85 is drivenby the output shaft 87 of motor 84 and supplies to the computer avoltage proportional to the rotational speed (rpm) of the motor. Thecomputer computes from these voltage, current and rpm signals an outputsignal on line 93, which signal is indicative of the motor torque. Thecomputer may compute the torque T in accordance with the followingformula found on page 673 of Circuits, Devices and Systems, by Ralph J.Smith, John Wiley Publishers, 3rd edition:

    T=3V.sup.2 s/ΩR.sub.2

where

where V is the applied voltage,

s is the slip,

Ω is the synchronous speed, and

R₂ is the rotor resistance.

This output signal is applied through a switch 94 to one input 96 of asummer 100. The other input of the summer is the voltage appearing onthe manually adjustable wiper arm 102 of a potentiometer resistor 104.The output of the summer on line 106 is then proportional to the motortorque as modified by the voltage on the wiper arm 102. This outputvoltage of the summer is applied to a suitable servo mechanism 108 whichthen changes the position of the lift mechanism of an implement attachedto the tractor.

The purpose of the circuit of FIG. 4 is to determine the torque on thedrive wheel and then in turn control the lift of the front or rear ofthe tractor in accordance with a predetermined amount of implementdraft. In conventional tractors, this result is generally achieved intwo ways. The first way is to sense the amount of draft or pull on thelift arms themselves and then raise or lower the lift arms to keep theimplement draft constant regardless of soil condition. The other way isto place a torque sensitive device in the drive line between the engineand drive wheels, which device in turn raises or lowers the implementthrough hydraulic lift arms to maintain constant draft regardless ofterrain or soil conditions.

It is clear that the electric torque monitoring control circuit shown inFIG. 4 is much simpler and more responsive than these correspondingprior art mechanical systems because the improved circuit immediatelysenses changes in the motor current and voltage as soon as the torquerequirements of the motor change. This voltage and current change ismonitored and used to control the raising or lowering of the lift armsto maintain a predetermined amount of implement draft or load on thedrive wheels of the tractor. Such a result is quite an advantage,because it helps control wheel spin when plowing, discing or doing othertypes of tillage work. The computer 90 operates on the parameters of theapplied A.C. voltage and current, frequency and rpm to calculate themotor torque. The frequency parameter is obtained from the measuredvoltage and/or current, and slip is a function of frequency and rpm. Thesynchronous speed for a particular motor is a function of the motordesign and frequency of the applied voltage. In practice, this computermay be a microcomputer or a suitable analog computing circuit.

The potentiometer wiper arm 102 is manually positioned by the tractoroperator to adjust the voltage applied to servo 108 to a value dependingupon operating conditions actually encountered in the field. The servocontrols the hydraulic or electric lift arms on the tractor inaccordance with the draft demand of the implement in a manner similar toprior mechanical systems mentioned above.

In the aforesaid copending application, there was described the use ofthe three-phase electrical power for driving auxiliary equipment oraccessories which are themselves driven by three-phase induction motors.However, the availability of this mobile, variable frequency three-phasepower source makes it practicable to drive other non-motor drivenaccessories. For example, the three-phase power can be used to energizethe electric grid of a crop dryer for drying grain at the same time thegrain is being combined. The power can also be used for the directelectrocution of weeds, or to drive a microwave weed-killing device.Electrical power can also be used to energize a laser for harvestingcrops, thereby eliminating the need of using sickles for cutting thecrop from the ground. Depending upon the nature of the electricallypowered device, the power can be derived directly from the output of thethree-phase alternator, from the variable frequency output of acycloconverter, or D.C. power is obtainable by rectification of the A.C.power. A pair of suitable power outlets or connectors 110 and 112 may bemounted on the rear of the tractor as shown in FIG. 1b; another pair maybe mounted on the front, and one of this pair is designated by thereference numeral 114 in FIG. 1a.

I claim:
 1. In combination:a steerable land vehicle havingground-engaging right and left traction means; a source of polyphaseelectrical power mounted on said vehicle; right and left cycloconvertermeans electrically coupled to said source for providing variablefrequency polyphase outputs; right and left polyphase induction motormeans energized by the power outputs from said right and leftcycloconverter means, respectively, and mechanically coupled to saidright and left traction means, respectively, to drive said vehicle;manually adjustable speed control potentiometer means having an inputterminal coupled to a reference voltage and also having an outputterminal for providing a master speed control signal; first signalsummer means coupled between said potentiometer output terminal and oneof said cycloconverter means; adjustable steering potentiometer meanshaving an input terminal coupled to the output terminal of said speedcontrol potentiometer and also having an output terminal for providing asteering control signal; said steering potentiometer being adjustable inresponse to the steering angle of said land vehicle so that saidsteering control signal is indicative of the magnitude and direction ofsaid steering angle; second signal summer means coupled between theother of said cycloconverter means and said output terminal of saidsteering potentiometer means so that said steering control signal isapplied to said second summer means; means for applying an inverted saidsteering control signal to said first signal summer means; whereby saidsteering control signal is effectively algebraically added with oppositepolarities to said master speed control signal in said first and secondsummer means, respectively, so that said right and left traction motormeans are driven at different relative speeds depending upon thedirection and magnitude of said steering angle.
 2. The combination ofclaim 1 wherein said steering potentiometer means comprises anadjustable wiper arm mechanically coupled to the steering mechanism ofsaid vehicle and electrically coupled to said output terminal of saidsteering potentiometer.
 3. The combination of claim 1 wherein said landvehicle has a material-transferring tunnel therein extendinglongitudinally of the vehicle between the front and rear thereof andpassing between said right and left traction means of the vehicle, andfurther comprising a longitudinally extending, vertically adjustabletunnel extension hinged to one end of said tunnel.
 4. The combination ofclaim 3 further comprising a second longitudinally extending, verticallyadjustable tunnel extension hinged to the other end of said tunnel. 5.The combination of claim 3 wherein said tunnel and tunnel extensioncontain at least two separate passageways therein for simultaneouslytransferring different materials through said passageways.
 6. Thecombination of claim 3 further comprising:at least one hollow-tubularaxle having an enlarged portion in the center thereof for mounting saidaxle for oscillating movement about said tunnel; and said right and lefttraction motor means being mounted within said axle in the opposite endsthereof.
 7. The combination of claim 1 further comprising torquemonitoring and implement draft control means for monitoring the torqueof a traction motor means and controlling the draft of an implementcoupled to said vehicle to maintain a predetermined draft of theimplement, said monitoring and control means comprising:means forobtaining electrical signals indicative of the rotational speed of saidtraction motor means, of the magnitude and frequency of the voltageapplied to said traction motor means and of the current flowing throughsaid traction motor means; computer means responsive to said signals toproduce an output signal indicative of the torque of said traction motormeans; manually adjustable potentiometer means for modifying said outputtorque signal to produce a servo signal indicative of the desiredimplement draft; and servo motor means, responsive to said servo signal,for adjusting the implement to a desired draft.
 8. The combination ofclaim 1 further comprising power outlet means electrically coupled tosaid power source for providing power to a non-motor driven electricalaccessory associated with said vehicle.
 9. The combination of claim 1further comprising third cycloconverter means having an inputelectrically coupled to said power source; andpower outlet meansconnected to the output of said third cycloconverter means for providingvariable frequency power to a non-motor driven electrical accessoryassociated with said vehicle.